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Economic theory indicates the need for nonlinear structural models to study medium-term and long-run dynamic behavior of an economy. This paper argues that economic systems can be better specified and estimated using differential-equation rather than difference-equation systems and briefly reviews the estimators of continuous models. This approach of specifying structural models on the basis of economic theory and institutional structure explicitly and then testing the underlying hypothesis to verify the structural form is contrasted with a general-to-specific approach of successively more restricted VARMAX processes. Previous analyses of stability about the steady state or fixed point in phase space are extended to more general attractors to allow an investigation of complexity in economic systems. The critical dependence of some attractors, and particularly strange attractors, on parameter values emphasizes the need for consistent, efficient estimation. A structural approach provides a rigorous alternative to using single time series to determine whether economic systems exhibit aperiodic or chaotic dynamical behavior.

The last twenty years have seen a marked slowdown of the Italian productivity growth rate. The literature has underlined the role of international factors, such as globalization and adoption of the euro. In this paper we emphasize the role and dynamics of capital accumulation investigating the impact of the introduction of information technology on capital and production in the Italian economy and the extent to which that is being affected by skills in the labour force. The model is specified and estimated as continuous-time general disequilibrium framework. It presents original features: it analyzes the effects of the introduction of the ICT technology on the Italian economy not in a partial equilibrium context of a single market but from a macro point of view where input markets interact; it does not assume that these markets instantaneously clear but rather that there are imperfections and frictions; it does not impose the condition that the economy necessarily converges to a steady state. The model behaves quite well in replicating the dynamics of the Italian economy. It also shows however that there remains some structural inefficiency that worsened in recent years. In fact, our main finding shows that there exists a permanent gap between "optimal" and actual output which increased in the latter part of the sample period. While a fraction of this gap can be attributed to unavoidable (market and non market) adjustment costs some is associated to efficiency losses

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